Some mobile devices (e.g., smart phones) include a haptic module that is configured to provide a tactile sensation such as a vibration to a user touching or holding the mobile device. The haptic module is a linear resonant actuator (LRA) that is connected mechanically to an input surface of the mobile device. Drive electronics coupled to the LRA cause the LRA to induce vibration which is transferred to the input surface so that the vibration can be felt by a user who is touching or holding the mobile device.
Some haptic module designs include a closed-loop controller that is configured to move a mass of the haptic module from its mechanical resting position to a sensor reference position (e.g., a sensor zero reference position) before processing a haptic waveform, and after processing the haptic waveform, move the mass back to its mechanical resting position to conserve power. The closed-loop controller ensures that the mass moves smoothly to its mechanical resting position to avoid a perceived “click” that occurs when the mass is moved too quickly. When the haptic module is embedded in a wearable device (e.g., a smart watch), holding the mass at the sensor reference position during orientation of the wearable device causes an undesirable transient or haptic “click” during controller turn off.